This section provides background information related to the present disclosure which is not necessarily prior art.
In use switching relays may fail “open” when the mechanical switch arms fail to close and the relay cannot conduct a current. This failure may result from arcing between a contact and a mechanical switch arm as the relay turns-off during operation. This arcing damages the relay contact and switch arm and may cause a reduction of a useful life of the relay.
The amount of arcing and hence the destructive potential of the arcing is proportional to the current passing through the relay as the relay is attempting to turn-off. It is desirable to turn-off the relay during a zero-cross time of the AC current flowing through the relay.
The prior art has attempted to turn-off the relay during a zero-cross in several ways. For example, it is known to detect a delay time between a relay turn-off signal and the relay's load current cycle time. Based on the determined delay time, the turn-off signal timing is adjusted to open the relay near a zero-cross point. However, because of signal bounce conditions, a rather complicated algorithm is required to ensure that the relay's true turn-off time is detected.
Another solution, includes using an optical sensor to detect the arcing and adjusting the turn-off timing until little or no arcing is detected. The optical sensor is a custom solution for an application that results in increased costs.
Still another prior art solution, includes randomly varying the turn-off signal timing to reduce the likelihood of repeated high arcing turn-off times, thus protecting against relay failure. However, varying the turn-off signal times only reduces the chances of significant arcing and does not eliminate or minimize arcing.
Therefore, it is desirable to have a relay turn-off control system that self-learns a turn-off duration time of the relay during operation and quickly determines a turn-off signal time so the relay contacts open during or near a zero-cross point of the AC signal flowing through the relay.